My ramblings about all things technical

Tag Archives: high availability

As started and introduced in my introductory posting around the VMware Knowledge Nuggets I am posting compact VMware knowledge nuggets which I hope will show people some unknown features or things they need to think about around choosing features and maybe even get some good discussions going via the comments section.

Using Percentage Based Admission Control and the usage of das.vmMemoryMinMB and das.vmCpuMinMHz.

This discussion stemmed from the twitter discussion I had with Ed Grigson a few weeks back as mentioned in my first posting (albeit a tangent off of it) . I commented that even if you use percentage based admission control it is still a good idea to configure the das.vmMemoryMinMB and das.vmCpuMinMHz advanced settings to provide a better idea when HA is doing the math for admission control and prevent overcommitment with a specified minimal amount of resources for each virtual machine.

Rather than re-cover what has been done and explained so well, the following two postings from Duncan Epping and Josh Odgers respectively cover it perfectly

Certainly something to keep in mind when doing designs and even something that you may determine is good to add to your existing environment. Although remember that admission control is not about resource management as described really well by Duncan Epping in his article here. Funnily enough I think a discussion I had with Duncan at the 2011 Europe VMworld around a customer using reservations with percentage based admission control for resource management caused him to create the posting.

Over the past few weeks I have had several discussions around VMware features and technologies via twitter where someone asked a question or made statement around a VMware vSphere feature and the subsequent discussions seemed to shed some light on things people either didn’t know or had forgotten.

So my idea is to create a series of blog postings trying to cover compact VMware knowledge nuggets which I hope will show people some unknown features or things they need to think about around choosing features and maybe even get some good discussions going via the comments section.

Does excluding VMs from HA exclude them from admission control calculations?

This question was posted by fellow London VMUG attendee Ed Grigson a few weeks back via twitter as shown below

Due to my aiming to reattempt my VCDX defence soon I have been reading and learning as much as is possible and had come across the answer to this during my reading of Duncan Epping and Frank Denneman’s vSphere 5.1 Clustering Deepdive book and responded to Ed with the answer which is No. Even if it is disabled within HA, it is still included in admission control calculations. So be mindful of leaving machines lying around in your cluster as depending of your admission control policy this could have varying impacts on your ability to power on machines.